Modular electric power distribution system

ABSTRACT

A modular electric power distribution system transmits power between a power source and control modules for power consumers. The system includes a power distribution unit mounted on each module and bridge assemblies which connect adjacent distribution units.

FIELD OF THE DISCLOSURE

The disclosure relates to a modular electric power distribution systemfor transmitting electric power between a power source and controlmodules for power consumers, which may be electric step motors. Power istransmitted in response to input signals received by circuitry in thecontrol modules. A number of types of electric power may be transmittedbetween the power source and the modules. Each type of power isdistributed to the modules depending upon the needs of power consumerscontrolled by the modules. Power may be transmitted from a powerconsumer back into the distribution system.

BACKGROUND OF THE DISCLOSURE

Electric power control modules supply power to step motors in responseto input signals received by the modules. Each module may supply anumber of different types of power. Conventionally, each module isconnected to a power source by heavy-duty power cables. Two cables arerequired for each type of power supplied to a module. Each moduleincludes a header connector which mates with a plug connector mounted onthe ends of each pair of power cables supplying a type of electric powerto the module. A number of power control modules are positioned togetherto facilitate connecting the modules to the power source and inspectionand servicing of the modules.

However, connecting each module to the power source using pairs ofheavy-duty cables for each required type of electric power is difficult,expensive and inconvenient. Sets of different length power cables mustbe cut, terminated and connected to the modules and to the power source.The large number of cables must be properly routed between the powersource and the control modules. This is a time-consuming and expensiveprocess. Servicing the cables and modules can be difficult.

Contact members on adjacent modules are connected by high voltage, highamperage bridge assemblies using one-piece copper conductors. Thesebridge assemblies have long conductor strips with copper U-bends at thestrip ends. The U-bends hold the copper strips on the contact members.

High amperage current flowed through conventional bridge assemblies canheat and weaken the copper U-bends sufficiently to reduce contactpressure between the conductor strips and the contact members. This canreduce current flow between modules.

Accordingly, there is a need for an improved modular power distributionsystem which efficiently connects a power source to a number of controlmodules without having to connect a pair of cables from the source toeach module for each type of power supplied to the module. The improvedsystem should include pairs of modular power conductors extendingbetween modules. The pairs of conductors for each type of power shouldbe connected to the power source by power cables extending to a first orend module only and should be connected to additional modules by pairsof series-oriented conductors having modular distribution units andbridge assemblies connecting adjacent distribution units. Thedistribution units should be removably mounted on the control modules,and the bridge assemblies should be easily and removably mounted on thedistribution units to facilitate installation and servicing.

There is also a need for an improved bridge assembly with copperconductors and heat-resistant springs which hold the copper conductorsagainst contact elements on the modules so that current heating of theconductors does not impair the springs and does not reduce current flow.

SUMMARY OF THE DISCLOSURE

One aspect of the disclosure is a modular electric power distributionsystem for connecting a power source to a number of control modules forelectric devices. The electric devices may be electric step motors orother types of electric devices.

Each control module requires one or more types of power supplied by thepower source. The types of power include AC and DC power and powerhaving different voltages and amperages. The modules may require up to300 or higher amps at a voltage as high as 600 or more volts. A pair ofpower cables for each type of power extends from the power source to anend control module. Pairs of conductors for each type of power extendfrom the end module to the other modules. Each conductor includes apower distribution unit on each control module and bridge assembliesextending between adjacent distribution units. The power distributionunits are connected to power contacts in the control modules.

Each type of power is transmitted from the source through the two powercables and along the distribution units and the bridge assemblies to thecontrol modules. Each module draws or returns power as required.Different length bridge assemblies connect control modules which arespaced apart different distances.

The distribution system can connect electric components other thancontrol modules for step motors.

Another aspect of the disclosure relates to an improved bridge assemblyfor forming electrical connections between distribution units onadjacent control modules. The bridge assembly may be used to connectother types of electric power components.

Each bridge assembly includes an insulating housing, two high-currentbridge conductors and two spring clips in the housing. The conductorsare made of highly conductive metal, which may be copper, with contactsat the ends of the conductors for forming electrical connections withdistribution units or other components. The spring clips are made fromheat-resistant metal, surround the contacts at the ends of the twobridge conductors and hold the conductors against plates in twodistribution units to provide reliable, low insertion force mounting onthe distribution units. The two conductors form two reliable electricalconnections between the distribution units. The conductors and springsin each bridge assembly are mounted in the insulated housing to form aone-piece assembly and to prevent arcing to adjacent components and toprevent inadvertent contact by a technician. Resistance heating of thespring clips does not reduce contact pressure.

A further aspect of the disclosure relates to an improved powerdistribution unit for mounting on a control module and formingelectrical connections between a power source, circuitry in the moduleand bridge assemblies extending to other modules. The distribution unitincludes upper level conductive plates with one or two upper bridgecontact portions, a single lower level module contact, and an insulatingbody. Distribution units are removably mounted on control modules byextending the lower level module contacts into the control modules forelectrical connection with circuitry in the modules. The ends of bridgeassemblies engage upper level contact portions to form part of anelongate power conductor extending past a number of control modules. Apair of conductors with distribution units and bridge assembliessupplies one type of power to a number of control modules.

The lower level module contacts in the distribution members may beclosely spaced to engage closely spaced power contacts in controlmodules. The upper level bridge contact portions in the distributionmembers may be widely spaced to engage relatively wide bridgeassemblies. The width of the bridge assemblies is determined by thespacing between bridge connectors in the assemblies, springs surroundingthe contact ends of the bridge connectors, and an insulating housingsurrounding the connectors and springs.

The distribution members in the distribution units with closely spacedmodule contacts may include widely spaced upper plates and lateral stepsbetween the module contacts and the plates. The plates engage the endsof the bridge assemblies from lower module contacts which engage powercontacts in the modules. The upper and lower portions of thedistribution members are fitted in an insulating housing.

The upper level bridge contact portions may be spaced apart the samedistance as the lower level contacts are spaced apart or may be spacedapart a greater or smaller distance than the lower level contacts,depending upon the requirements of a particular distribution system.When the spacing is different, distribution members may include lateralshift steps to provided offsets. The amount of offset in individualdistribution members may increase across the distribution unit to spacethe upper portions evenly for engagement with evenly spaced bridgeassemblies and to space the module contacts evenly for engagement withevenly spaced power contacts.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a modular electric power distributionsystem;

FIG. 2 is a top view of FIG. 1;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 2;

FIG. 4 is a sectional view taken along line 4-4 of FIG. 2;

FIG. 5 is a side view of a bridge assembly above a power distributionunit showing an alternative distribution unit;

FIG. 6 is a sectional view taken along line 6-6 of FIG. 5;

FIG. 7 is a sectional view similar to FIG. 6 showing the bridge assemblyengaging the distribution unit;

FIG. 8 is an exploded view of an end power distribution unit;

FIG. 8A is a top view of the power distribution unit shown in FIG. 8;

FIG. 9 is a top view of power distribution members in the distributionunit of FIG. 8;

FIGS. 10, 11 and 12 are exploded views of power distribution units;

FIG. 13 is an exploded view of a bridge assembly;

FIG. 14 is a side view of a power conductor used in a bridge assembly;

FIG. 15 is a bottom view of a cover taking the direction of line 15-15of FIG. 13; and,

FIG. 16 is a sectional view taken along line 16-16 of FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a modular electric power distribution system 10. TheFIG. 1 system forms two conductor electrical connections between anelectric power source 12 and four or more control modules 14. Eachcontrol module includes a rectangular body 16 with a top surface 18 anda mounting opening 20 formed in top surface 18. The openings 20 arealigned in a row on surfaces 18. Power contacts 22 are located inmodules 14 below openings 20 for forming electrical connections withcontacts in the lower portions of power distribution units 24 and 26which extend into openings 20.

Each control module 14 is connected to an electric step motor or otherpower consumer. The module includes an actuator circuit which determineswhen power is required to be supplied to the step motor or consumer, orwhen power from the step motor or consumer is returned back to system10. The components of modules 14 and the actuator circuits are notillustrated.

The power distribution system 10 includes pairs of elongate powerconductors 28 extending across the tops of modules 14. In FIG. 1, thesystem includes four conductors 28 to communicate two types of electricpower between the source 12 and the modules. Two conductors 28 arerequired for each type of power distributed by system 10. The system 10uses as many pairs of conductors 28 as required to supply needed typesof power to and receive power from the control modules.

Power may be AC or DC and may be supplied at high amperage which may beas great as 100 amperes. The power may have a voltage as high as 600volts.

Each conductor 28 passes through an end power distribution unit 24mounted on end module 14 and a number of like power distribution units26 mounted on other modules 14. Each conductor 28 also includes a numberof bridge assemblies 36 which connect adjacent pairs of powerdistribution units 24 and 26. End unit 24 on end module 14 is connectedto power source 12 by heavy-duty, high amperage and high voltage powercables 34. In FIG. 1, units 24 and 26 are shown partially inserted intomodules 14.

The conductors 28 are connected to source 12, extend throughdistribution units 24 and 26 on the modules and through bridgeassemblies 36 between modules. Each distribution unit is connected to apower contact 22 in a module. Adjacent pairs of conductors 28 supply onetype of power to the modules and can receive the same type of power backfrom the modules.

Each power distribution unit 26 includes an insulated body with moldedplastic upper contact housing 40 latched onto molded plastic lowercontact housing 42. See FIG. 10. Metal power distribution members 44 arefitted in recesses 46 in the upper plate housing 40 and in recesses 48in the lower contact housing 42. Each member 44 includes a flat, thickupper plate 50, a central thick lower plate 52, a lateral shift step 54between the plates and a disconnect pin or module contact 56 on thebottom of the plate 52. The plates are formed from copper to conducthigh amperage current. In some units, steps 54 may not be used so thatthe upper and lower plates are aligned.

Recesses 46 are spaced across the upper contact housing 40 for plates50, and recesses 48 are spaced across in housing 42 for plates 52.Recesses 46 in upper plate housing 40 have a width sufficient to receivethe relatively wide ends of the bridge assemblies 36 and form electricalconnections with a pair of power conductors in each bridge assembly. Acentral opening 58 is provided in housing 42 at the bottom of eachrecess 48.

The top of each upper plate 50 includes upper contact portion 60 withcontact surfaces 61 on both sides of portions 60. The contact portions60 are located on opposite plate ends for forming electrical connectionswith bridge assemblies 36 extending between adjacent distribution units.The distribution members 44 are formed from thick copper plate stock forreliable flow of high amperage and high voltage current throughdistribution system 10.

Power contact 56 on lower plate 52 is fitted in a recess in the bottomof lower housing 42 above opening 58. The power contacts 56 are spacedcloser together than upper plates 50 in the upper and lower housings.The different spacing is achieved by lateral shift or offset steps 54between plates 50 and 52. The contacts 56 are mounted on one side oflower plate 52. The offset steps 54 and offset contacts 56 assure thatupper plates 60 are uniformly spaced to fit in recesses 46 and 48 andthat contacts 56 are uniformly spaced, closer together than plates 50,and fit in the bottoms of recesses 48. The upper portions of recesses 48are spaced to receive the lower portions of upper plates 50 and arelaterally offset from the bottoms of the recesses which receive thelower plates 52 and offset contacts 56.

Offsets or steps 54 on the two members 44 on one side of unit 32 locatecontacts 56 closer to the center of the housing than upper plates 50.The offsets 54 on the two members 44 on the other side of unit 26 alsolocate the contacts 56 closer to the center of the housing than plates50. Plates 50 are uniformly spaced, and the contacts 56 are uniformlyspaced. This means that the offsets for the inner distribution membersare smaller than the offsets for the outer distribution members 44. Theouter two distribution members 44 are identical but are rotated 180°,and the inner two distribution members 44 are identical but are rotated180° to provide desired uniform spacing of the contacts 56 and uniformbut wide spacing of plates 50.

Steps 54 shown in FIG. 10 extend horizontally across members 44. Ifdesired, contacts 56 may be mounted on offset cut-out lower plates inmembers 44 which are connected to the upper plates by verticallyextending lateral shift steps.

The power contacts 56 illustrated in distribution unit 26 may be mountedon either side of the offset lower plates 52 of members 44 to providelateral shift.

Distribution units 26 have four power distribution members 44 with ahorizontal lateral shift step in each member 44. The steps space plates50 from contacts 56. Alternatively, a power distribution unit may haveone flat center distribution member 44 without a lateral shift step. Theplate 50 for the center member 44 would extend above a central contact56, without a lateral shift step. The plates 50 of the member 44 on oneside of the center member would have an outer lateral shift step, asdescribed. The plates 50 of the member on the other side of the centermember would have an outer lateral shift step as described, and themembers outside these members would have outer lateral shift stepsgreater than those of the adjacent members in order to maintain uniformspacing between plates 50 and uniform but closer spacing of the contacts56 at the bottoms of the plates.

If desired, a distribution unit may have a side power distributionmember without a lateral shift step and progressively greater lateralshift steps in members to one side of the no-shift member.

FIG. 8 is an exploded view of end power distribution unit 24, and FIG.8A is a top view of end power distribution unit 24. Unit 24 includes aninsulating body 64 with upper plate housing 66 and lower contact housing68. Four metal power distribution members 70 are positioned in the body.Members 70 are like previously described members 44 with the exceptionthat each copper upper plate 72 includes opposed contact surfaces 74 atone plate end and a vertically extending power contact tab 76 at theopposite end of the plate. The upper and lower housings 66 and 68 aresimilar to previously described housings 40 and 42 with the exceptionthat side cavities 78 are provided in housing 66 to receive tabs 76 andcable clamps 80 fitted on the tabs. The clamps are seated in cavities 78with tabs 76 extending through central openings of the clamps. Cover 82is latched onto housing 66 over the cable clamps 80 and includes spacedcable insertion openings 84 above the clamps.

Stripped ends of power cables 34 are extended through the openings 84 incover 82 and into the openings in the clamps. Electrical connections areformed between the power cables and the distribution members 70 bytightening clamp screws 86 which threadably engage the clamps. When eachscrew is tightened, a cable is clamped against a tab 76, and anelectrical connection is formed between the cable and a member 70.

In power distribution unit 24, power contacts 88 on members 70 arelocated in recesses in the bottom of housings 68 and are spaced closertogether than the plates 72 by lateral shift steps 90 in members 70, aspreviously described.

Tabs 76 and cable clamps 80 are wider than plates 72. The tabs 76 on theoutermost plates 72 are connected to the plates by 90° outward bends 92and extend outwardly from the plates. See FIG. 9. The tabs 76 on theinner two plates 72 are connected to the plates by 90° inward offsetbends 94 and extend outwardly from the plates. The inner tabs 76 arespaced a distance 96 out from the ends of the plates 72, beyond theouter tabs 76, to provide increased clearance between inner and outertabs. Comparable clearance 98 is provided between the inner tabs atbends 94. Clearances 100 are provided between inner tabs 76 and bends92. Positioning the tabs and wire clamps in spaced, wide cavities 78with clearances separates members 70 and allows the plastic wallsbetween the members to prevent arcing or creepage discharge betweenadjacent members when high amperage and high voltage current isdistributed by system 10. The plastic walls of insulating body 64 arenot shown in FIG. 9. The bends 92 and 94 space the upwardly extendingtabs 76 across unit 24 to fit in cavities 78.

Distribution members 70 are inserted into lower contact housing 68,following which upper plate housing 66 is positioned on housing 68 withplates 72 in plate recesses 108 and 110 and tabs 76 extending intocavities 78. The latch openings 106, on the ends of housing 66, snaparound latch projections 112 to secure housings 66 and 68 together. Theclamps 80 are fitted in cavities 78, and cover 82 is latched onto upperplate housing 66.

FIGS. 11 and 12 are exploded views of power distribution units 172 and174, which are similar to unit 26. Each unit includes a two-pieceinsulating body with upper and lower contact housings like body 38. Eachinsulating body has interior recesses and surrounds two powerdistribution members.

In FIG. 11, power distribution members 176 are like members 44 with theexception that the lower plate portions 178 are located inwardly of theupper plate portions 180 by inward lateral shift steps 182. Modulecontacts 184 are mounted on the inner sides of lower plate portions 178.

In FIG. 12, the lower plate portions 186 are connected to upper plateportions 188 by outer, horizontal lateral steps 190, and the modulecontacts 192 are mounted on the inner sides of the lower portions, as indistribution unit 26 illustrated in FIG. 10.

In distribution units 24 and 26, the module contacts 56 and 88 aresocket contacts and engage pin-type power contacts 22 in the modules. Asillustrated in FIGS. 4, 6 and 7, socket contacts on the lower plateportions may be replaced by pin-type contacts to engage socket contactsin the modules.

FIG. 13 is an exploded view of a bridge assembly 36. Bridge assembly 36includes two flat copper conductors 114, two stainless steel springclips 116 which surround the ends of conductors 114, and a plastichousing 118, also shown in FIG. 1, which surrounds the conductors andclips. The housing 118 includes molded plastic housing base 120 andcover 122.

Each conductor 114 is formed from thick, conductive copper sheet stockand includes an elongate, flat conductor strip 124 extending along thelength of assembly 36 with three contact arms 126 extending downwardlyat 90° from each end of each conductive strip 124. Slots 128 separateadjacent arms 126.

Clips 116 are formed from flexible, heat-resistant stainless steel. Eachclip includes U-shaped upper portion 130 with three spaced individualspring arms 132 extending downwardly from the lower end of each side ofportion 130. The lower ends of arms 132 are bent inwardly to providepressure ends 134 located inwardly from arms 132. See FIGS. 6 and 7.When clips 116 are positioned on the ends of conductor strips 124, ends134 of spring arms 132 engage the lower ends of contact arms 126.

Plastic housing base 120 includes an elongate, circumferential wall orshell 136 which surrounds conductor strips 124 and top portions of clips116. Base 120 includes two three-sided arm shields 138 at each end ofwall 136. The open sides of shields 138 at each end of wall 136 faceeach other and partially surround contact arms 126 and spring arms 132when the strips and clips are inserted into housing 118. Contactprojections 140 are provided on the inner surfaces of the lower ends ofcontact arms 126.

Contact clips 116 are fitted on the ends of the two conductors 114 witheach clip arm 132 overlying a contact arm 126, as illustrated in FIGS. 6and 7. The spring arms 132 individually bias the contact arms 126inwardly to form reliable individual electrical connections with theplates 50 and 72 in distribution units 24 and 26 when assemblies 36 aremounted on the units. Rectangular wall or shell 136 surrounds conductorstrips 124. The three-sided shields 138 at each end of the shell 136partially surround arms 126 and 132 while allowing each arm 126 tocontact plates 50 and 72 in the distribution units. The shields and arms126 and 132 are separated by central slots 142. Each slot receives acontact portion of a copper plate 50 or 72 when the bridge assembly ismounted on the distribution units. Three separate spring-backed andreliable electrical connections are formed between each conductor 114and each plate 50, 72.

Housing base 120 includes a central bar 144, shown in FIGS. 6 and 7,which is located inside shell 136 and extends between the ends of theshell midway between the sides of the shell. Bar 144 is between tworecesses 146, each located between the bar and one side of base 120.Conductor strips 124 and the sides of upper clip spring portions 130 arepositioned in recesses 146.

Cover 122 includes elongate top wall 148 which closes the top opening inbase 120. End lock tabs 150 extend downwardly from the ends of wall 148.Two side lock tabs 152 extend downwardly from the sides of wall 148between a pair of side walls 154 at each end of top wall 148. A contactclip location projection 156 extends inwardly from each end of the topwall 148 between side walls 154. Projections 156 and walls 154 definerecesses for locating strips 124 and portions 130 of contact clips 116in housing 118.

Conductors 114, with clips 116 fitted around the ends of the conductorsand spring arms 132 overlying contact arms 126, are positioned in base120 with the upper ends of the spring arms and contact arms in recesses146 and bar 144 separating conductors 114. Cover 122 is then latchedonto base 120 with projections on end and side tabs 150, 152 latchedinto openings formed in shell 136. Contact arms 126 extend parallel tothe sides of assembly 36, and conductor strips 124 fit between the clips116 and bar 144. Spring clips 116 are not stressed. The conductors 114are loosely confined in housing 118.

Modular electrical power distribution system 10 is installed on a numberof side-by-side power control modules by extending an end powerdistribution unit 24 in opening 20 in an end module 14 and fitting powerdistribution units 26 in the openings in the remaining modules. Powercontacts 56 on the units 24 and 26 make electrical connections withmodule contacts 22. Power cables 34 are secured to the powerdistribution members 70 in unit 24, as previously described.

Next, a pair of bridge assemblies 36 is mounted on adjacent distributionunits 24, 26 for each type of power to be supplied to or received frommodules 14, as illustrated in FIG. 1. The assemblies 36 may havedifferent lengths in order to connect distribution units mounted ondifferent width modules.

Bridge assemblies 36 connect adjacent units 24 and 26. Each conductor114 in the assembly forms an electrical connection between the copperplates in the units independent of the other conductor. The arm shields138 at each end of bridge assembly 36 extend into recesses 46, 108 sothat shields 138, contact arms 126 and spring arms 132 are moved downand onto a plate. The thickness of the plate is greater than the restspacing between contact projections 140. During insertion, the beveledlead ends 160 of arms 126 engage plastic guiderails 162 which overly topedges 164 of the copper plates in units 24 and 26. See FIGS. 6 and 7.Guiderails 162 extend between the end walls of the upper housings 40 and66. The rails 162 are beveled and spread arms 126 apart for movement ofcontact projections 140 onto the plates in the distribution units. Theconductors 114 rotate in housing 118 during insertion into thedistribution units.

Spreading of arms 126 elastically flexes individual spring arms 132outwardly to provide reliable, low-level contact pressure holding eachprojection 140 against the copper plates and forming three independentelectrical connections between the plates and each end of each conductor114. The guiderails 162 provide touch safety when a bridge assembly 3 isnot installed.

During use of system 10, high voltage and high amperage current flowsalong the bridge assemblies 36 between adjacent distribution units. Thecurrent flow may be sufficient to increase the temperature of the copperconductors 114. The contact clips 116 are formed from a heat-resilientmetal, which may be stainless steel, which does not lose its springproperties when heated by conductors 114. This means that heating of theconductors does not decrease the contact pressure between conductors 114and the plates in the distribution units and does not impair currentflow.

Conventional, high-current bridge assemblies use copper conductor stripswhich are joined together at the ends of the assemblies by integralcopper U-bends. The U-bends hold the contacts at the ends of theassembly against inserted blades. High-current resistance heating ofthese conductors can heat and weaken the U-bends to undesirably reducecontact pressure with plates inserted between the ends of theconductors.

Each end of each conductor 114 is electrically connected to each plateby three independent electrical connections at contact projections 140.A separate spring arm 132 holds each contact arm against the plate atthe connection so that possible degradation of one connection does notimpair other connections.

Each conductor 114 in a bridge assembly 36 conducts electricity betweentwo plates. Typically, each conductor conducts one-half of theelectricity conducted by the assembly.

What we claim as our invention:
 1. A power distribution system fortransmitting electricity between power contacts in spaced first andsecond modules, the system comprising first and second powerdistribution units and a plurality of bridge assemblies extendingbetween the power distribution units; each power distribution unitcomprising a dielectric body, a plurality of electrically conductivedistribution members in the dielectric body, each distribution memberhaving a module contact at a first side of the dielectric body and acontact plate at a second side of the dielectric body, the contact platecomprising two opposed sides, each side comprising a contact surface,the first power distribution unit to be mounted on a first module withthe module contact engaging a power contact in the first module, thesecond power distribution unit to be mounted on a second module with themodule contact engaging a power contact in the second module; eachbridge assembly comprising a dielectric housing, a first elongateconductive member in the dielectric housing, a second elongateconductive member in the dielectric housing, a first contact at each endof the first conductive member, a second contact at each end of thesecond conductive member, and openings in the housing adjacent suchcontacts; each bridge assembly removably mounted on the first and secondpower distribution units with a plate on the first power distributionunit extending through the opening at one end of the housing and onecontact surface of the plate engaging an adjacent first contact on thefirst conductive member and the other contact surface of the plateengaging an adjacent second contact on the second conductive member, aplate on the second power distribution unit extending through theopening at the other end of the housing and one contact surface of theplate engaging an adjacent first contact on the first conductive memberand the other contact surface of the plate engaging an adjacent secondcontact on the second conductive member, wherein the first and secondconductive members of each bridge assembly and a distribution member ineach distribution unit form an electrical connection between powercontacts in the first and second modules.
 2. The system as in claim 1wherein the plates in each power distribution unit are flat and parallelto each other, and the plates are uniformly spaced apart, and thecontacts are uniformly spaced apart.
 3. The system as in claim 2 whereinthe spacing of the plates is different than the spacing of the contacts.4. The system as in claim 1 wherein one plate includes a lateral shiftstep.
 5. The system as in claim 1 wherein one module contact is mountedon a side of a plate.
 6. The system as in claim 1 wherein the first andsecond sides of each dielectric body are opposed to each other.
 7. Thesystem as in claim 1 wherein each plate includes first and second spacedcontact portions and each bridge assembly contact engages a first platecontact portion, wherein the second plate contact portions are availablefor engagement by another bridge assembly.
 8. The system as in claim 1wherein each dielectric body includes a recess for each plate and arecess for the module contact on such plate, and one plate recess islaterally spaced from its associated contact opening.
 9. A powerdistribution system for transmitting electricity between power contactsin spaced first and second modules, the system comprising first andsecond power distribution units and a plurality of bridge assembliesextending between the power distribution units; each power distributionunit comprising a dielectric body, a plurality of electricallyconductive distribution members in the dielectric body, eachdistribution member having a module contact at a first side of thedielectric body and a contact plate at a second side of the dielectricbody, the first power distribution unit to be mounted on a first modulewith the module contact engaging a power contact in the first module,the second power distribution unit to be mounted on a second module withthe module contact engaging a power contact in the second module; eachbridge assembly comprising a dielectric housing, a first elongateconductive member in the dielectric housing, a first contact at each endof the conductive member, and openings in the housing adjacent suchcontacts; each bridge assembly removably mounted on the first and secondpower distribution units with a plate on the first power distributionunit extending through the opening at one end of the housing andengaging an adjacent contact on the conductive member and a plate on thesecond power distribution unit extending through the opening at theother end of the housing and engaging an adjacent contact on theconductive member, wherein each bridge assembly and a distributionmember in each distribution unit form an electrical connection betweenpower contacts in the first and second modules, and wherein each bridgeassembly includes a heat-resistant spring in the housing at eachcontact, wherein each spring biases a contact against a plate tomaintain an electrical connection therebetween essentially independentof the temperature of the conductive member in the housing.
 10. Thesystem as in claim 9 wherein each bridge assembly comprises a secondelongate conductive member extending along the first elongate conductivemember, the second elongate conductive member including a second contactat each end thereof; and, two heat-resistant clips surrounding the endsof the first and second elongate conductive members, each clip havingresilient arms engaging the conductive members to bias the contactsagainst a plate between the contacts.
 11. The power distribution systemas in claim 10 wherein each elongate conductive member includes aplurality of contact arms at each end thereof, each clip surrounding theconductive members and engaging the arms.
 12. The system as in claim 11wherein each distribution unit dielectric body includes a guard railoverlying each plate, each guard rail between the elongate conductivemembers.
 13. A power distribution system for transmitting electricitybetween a power source and power contacts in a plurality of modules, thesystem comprising a power distribution unit associated with each moduleand a plurality of bridge assemblies extending between adjacent powerdistribution units; each power distribution unit comprising a dielectricbody and a plurality of electrically conductive distribution members inthe dielectric body, each distribution member including a plate awayfrom the associated module and a module contact engaging a power contactin the associated module, said plates extending parallel to each other,each plate including opposite sides with a first contact surface on oneside and a second contact surface on the other side; two bridgeassemblies extending between pairs of power distribution units onadjacent modules, each bridge assembly including a dielectric housing,first and second elongate conductors in the housing, a pair of firstcontacts at the ends of the first elongate conductor, and a pair ofsecond contacts at the ends of the second elongate conductor, each firstcontact engaging a first contact surface and each second contactengaging a second contact surface to form electrical connections betweenadjacent distribution units.
 14. The power distribution system as inclaim 13 wherein the spacing between the plates in one distribution unitis different than the spacing between the module contacts in thedistribution unit.
 15. The power distribution system as in claim 14wherein the plate of each distribution member has opposite sides spacedlaterally from each other, the module contact of such distributionmember spaced laterally from the plate.
 16. The power distributionsystem as in claim 13 including a guard rail over each plate.
 17. Apower distribution system for transmitting electricity between a powersource and power contacts in a plurality of modules, the systemcomprising a power distribution unit associated with each module and aplurality of bridge assemblies extending between adjacent powerdistribution units; each power distribution unit comprising a dielectricbody and a plurality of electrically conductive distribution members inthe dielectric body, each distribution member including a plate awayfrom the associated module and a module contact engaging a power contactin the associated module, said plates extending parallel to each other,each plate including spaced contact surfaces; two bridge assembliesextending between pairs of power distribution units on adjacent modules,each bridge assembly including a dielectric housing and a first elongateconductor in the housing, and a pair of contacts at the ends of theelongate conductor, each contact engaging a contact surface to formelectrical connections between adjacent distribution units, and whereineach bridge assembly includes a second elongate conductor in thedielectric housing with a pair of contacts on the ends of the secondelongate conductor, said elongate conductors formed from highlyconductive metal, and including a pair of heat-resistant spring clips,each spring clip surrounding each end of said elongate conductor to biasthe contacts against distribution member plates inserted therebetween.18. The power distribution system as in claim 17 including a pluralityof contact arms at each end of each elongate conductor and a pluralityof spring arms at each side of each clip, said spring arms overlyingsaid contact arms to individually bias the contact arms against theplates.
 19. A power distribution system for transmitting electricitybetween a power source and power contacts in a plurality of modules, thesystem comprising a power distribution unit associated with each moduleand a plurality of bridge assemblies extending between adjacent powerdistribution units; each power distribution unit comprising a dielectricbody and a plurality of electrically conductive distribution members inthe dielectric body, each distribution member including a plate awayfrom the associated module and a module contact engaging a power contactin the associated module, said plates extending parallel to each other,each plate including spaced contact surfaces; two bridge assembliesextending between pairs of power distribution units on adjacent modules,each bridge assembly including a dielectric housing and a first elongateconductor in the housing, and a pair of contacts at the ends of theelongate conductor, each contact engaging a contact surface to formelectrical connections between adjacent distribution units, and whereinone power distribution unit includes cable contacts on the platesthereof for engaging power cables connected to a power source.
 20. Thepower distribution system as in claim 19 wherein each cable contactincludes a contact tab and a cable clamp for securing a conductor of apower cable against the tab.
 21. The power distribution system as inclaim 20 including 90° bends between said plates and said tabs.
 22. Thepower distribution system as in claim 21 wherein one bend is an outwardbend.
 23. The power distribution system as in claim 21 wherein said bendincludes an inward bend.